Oxidative stress causes rapid membrane translocation and in vivo degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase.

We have studied the turnover of an abundant chloroplast protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rbu-P2 carboxylase/oxygenase), in plants (Spirodela oligorrhiza and Triticum aestivum L.) and algae (Chlamydomonas reinhardtii and C. moewusii) induced to senesce under oxidative conditions. Rbu-P2 carboxylase/oxygenase activity and stability in vivo were found to be highly susceptible to oxidative stress, resulting in intermolecular cross-linking of large subunits by disulfide bonds within the holoenzyme, rapid and specific translocation of the soluble enzyme complex to the chloroplast membranes, and finally protein degradation. The redox state of Cys-247 in Rbu-P2 carboxylase/oxygenase large subunit seems involved in the sensitivity of the holoenzyme to oxidative inactivation and cross-linking. However, this process did not drive membrane attachment or degradation of Rbu-P2 carboxylase/oxygenase in vivo. Translocation of oxidized Rbu-P2 carboxylase/oxygenase to chloroplast membranes may be a necessary step in its turnover, particularly during leaf senescence. Thus, processes that regulate the redox state of plant cells seem closely intertwined with cellular switches shifting the leaf from growth and maturation to senescence and death.